Most solar cells on the market today are a sandwich of a solar collector below a clear protective substrate, most often plain glass. This invention teaches advanced optics positioned directly above solar collector(s) of a complementary design, whose objective is to increase the level of solar energy harvested by those cells while, depending on the application, predominantly maintaining visual transparency of the device.
Standard lenses are rotationally symmetrical and often spherical. Another commonly used lens is the Fresnel lens. These are not the optimum configuration to capture the maximum solar energy from the sun's arch overhead in the sky. A stationary lens system optimized to capture the maximum sunlight during a day from the sun needs an asymmetrically aspheric surface topology. This invention employs an aspheric lens because it has the widest acceptance angle. The asymmetry is required to optimize the acceptance of sunlight from various latitudes when the lens is part of a vertical structure.
Aspheric means that the radius of curvature along a lens “meridian” (which is an imaginary line on the lens surface passing through the geometric center of the lens, analogous to a geographic meridian) need not be a constant. Indeed, the lens curvature flattens progressively from the geometric center to the periphery. Asymmetric means that the profile of the lens curvature along a half-meridian is not the same as (i.e., it is not a mirror image of) the other half of the same meridian. The degree to which lenses are aspheric and/or asymmetric needs to vary depending on the position on the earth (by application) to maximize the total solar energy gain.